1 Field of the Invention
The present invention generally relates to the blow molding of containers used for containing liquid and viscous products. In particular, the present system relates to blow molding systems where the containers are simultaneously blow molded and filled with the product.
2 Description of Related Art
Plastic containers are commonly used for the packaging of various products, including liquid products and viscous product. One of the most common forms of plastic container is the blow molded plastic container, which is often formed of a polyester material such as polyethylene terephthalate (PET). Blow molded plastic containers are typically formed by placing a heated preform into a blow mold and then inflating the preform with air until the preform contacts the interior surfaces of the mold cavity, which define the final shape of the desired container. Once the inflated preform has been held against the interior surfaces of the mold cavity by the pressure of the blow air for a length of time sufficient to “freeze” the plastic, the molded container is removed from the mold.
The molded containers then transported to the location where the container will be filled with the intended product and labeled. This may include the packaging and shipping of empty containers to a remote location or may involve the transfer of the containers to a local facility where these final steps occur before the finished product is shipped to a retailer or end-user.
With the above method, blow molding and filling are distinct and separate steps in the process of producing a product filled container. A new process involves the use of the product itself in the blow molding of the container. Instead of utilizing air as the blowing medium, this new process utilizes the liquid or viscous product that is to be retained within the container as the blowing medium. The container is therefore simultaneously blow molded and filled. As used herein, this type of molding is referred to as liquid blow molding or hydraulic molding.
In traditional blow molding, after the heated preform has been placed in the mold cavity, a stretch rod is often advanced within the preform to longitudinally stretch the preform before any significant radial expansion of the preform is undertaken. The stretch rod will typically remain within the preform during radial expansion, and is retracted prior to removal of the resultant container.
One concern of hydraulic molding is the contamination of the preform since product is immediately introduced into the preform during the hydraulic molding process. Since the stretch rod and blow nozzle are in contact with product used to hydraulically mold the container, there is a concern that residual product on the stretch rod or blow nozzle may become contaminated over time. Additionally, there is the possibility that residual product on the stretch rod or nozzle may be drip onto a heated preform, prior to dispensing of the hydraulic blowing medium, and that contact of this residual product with the heated preform may result in a local portion of the preform exhibiting defects after hydraulic molding. One possible defect is a cosmetic discoloration of the resultant container. Another, more significant defect is that the molded container may experience blow out, wherein a hole is formed in the container during the hydraulic molding process, resulting in the hydraulic blowing medium coming into contact with the interior surfaces of the mold and requiring extensive cleaning of the mold cavity. A hydraulic molding machine would obviously experience significant down time during the resultant cleaning process.